This reduction was due to the Lunar New Year holiday at the end of January this year, reducing the number of working days, said GSO economists.
The mining sector saw the strongest reduction of 18.4 percent year on year in IIP in the first month this year.
The processing and manufacturing sector, responsible for a large part of domestic industrial production, reported IIP reduction of 4.8 percent while the IIP of electricity production and distribution fell by 3.5 percent.
Meanwhile, the IIP of the water supply and waste-sewage treatment sectors rose by 1.6 percent year on year.
Many industrial products had a strong reduction in output, such as automobiles (38 percent), sugar (30.4 percent), motorbikes (22 percent), liquefied petroleum gas (21.2 percent), coal (18.5 percent), milk powder (18.4 percent) and raw steel (15.1 percent).
However, some industrial products posted growth in production, including metal ore (34.3 percent), steel bars and steel angle bars (23.5 percent) and mobile phones (10.4 percent).
GSO officials said production is expected to recover soon because, in January, the number of labourers in industrial enterprises increased by 0.5 percent year on year.